BOURNS SinglFuse SMD Fuses User Guide

BOURNS SinglFuse SMD Fuses User Guide

A properly selected fuse is widely regarded as the most effective way to safeguard a circuit against potentially catastrophic short circuit events. To this end, Bourns® SinglFuse™ SMD Fuses represent a robust and reliable solution that provides effective overcurrent protection to circuits. These fuses are available in a range of standard SMD packages that accommodate a variety of application needs, with sizes spanning from 0402 to 3812. The fuses are engineered using seven distinct technologies that incorporate board voltage and current ratings, operating temperature ranges, and fusing characteristics, making them an attractive option for designers seeking a versatile and customizable solution. A comprehensive overview of Bourns® SinglFuse™ SMD Fuses portfolio is outlined in the SinglFuse™ SMD Fuse Product Line Chart below. To facilitate the selection of the most appropriate fuse from this range, this article presents key considerations to guide the selection process. To enhance the value of these considerations, a practical example is presented to illustrate their application in real-world scenarios.

SINGLFUSE SMD FUSE PRODUCT LINE CHART

*Meets Bourns’ internal AEC-Q200 equivalent test plan.

When selecting a SinglFuse™ SMD Fuse, several factors must be considered, including the normal operating current in the circuit, the maximum operating voltage (AC or DC) in the circuit, the ambient temperature during normal operation, the overload current and fusing time required for the fuse to open, the maximum interrupting current, surge currents, inrush currents, and start- up currents, physical dimension limitations, and safety agency approvals such as UL, CSA, TÜV, or PSE.

NORMAL OPERATING CURRENT AND RATED CURRENT

Fuses are devices that are sensitive to temperature, and their ratings for current, voltage, and interrupting capability are commonly tested under ambient temperature conditions of 25 °C. In order to prevent nuisance tripping, it is recommended that fuses be operated at a maximum of 75 % of their rated current under these conditions.

For instance, SF-0603SP200R-2 is rated at 2 A at 25 °C, and it is advised not to exceed an operating current of 1.5A.

Electrical Characteristics

Model| Rated Current (A)| Resistance (Ω) Typ. 1| Rated Voltage 1| Interrupting Rating| Typical I 2t (A2s)2| Agency Recognition
---|---|---|---|---|---|---
cUL: E198545
SF-0603SP100R-2| 1.0| 0.115| 63 VDC| 50 A @ 63 VDC| 0.059| ✓
SF-0603SP150R-2| 1.5| 0.059| 0.13| ✓
SF-0603SP200R-2| 2.0| 0.033| 0.21| ✓
SF-0603SP300R-2| 3.0| 0.0159| 0.71| ✓
SF-0603SP400R-2| 4.0| 0.01| 0.96| ✓
SF-0603SP500R-2| 5.0| 0.00677| 2.05| ✓
SF-0603SP600R-2| 6.0| 0.0063| 3.47| ✓
SF-0603SP700R-2| 7.0| 0.0047| 5.04| ✓
SF-0603SP800R-2| 8.0| 0.0043| 6.5| ✓

Notes:

1. Resistance value measured with ≤10 % rated current at 25 °C ambient. Tolerance ±25 %.
2. Melting I2t calculated at 0.001 second pre-arcing time

RATED VOLTAGE AND APPLICATION VOLTAGE

The rated voltage of a fuse is the maximum voltage at which it can safely interrupt a short circuit current within its rated current.
It must be greater than the maximum operating voltage of the circuit. Therefore, the SF-0603SP200R-2 fuse, with a rated voltage of 63 VDC, can be utilized in circuits where the maximum operating voltage is below 63 VDC.

Model| Rated Current (A)| Resistance (Ω) Typ. 1| Rated Voltage 1| Interrupting Rating| Typical I 2t (A2s)2| Agency Recognition
---|---|---|---|---|---|---
cUL: E198545
SF-0603SP100R-2| 1.0| 0.115| 63 VDC| 50 A @ 63 VDC| 0.059| ✓
SF-0603SP150R-2| 1.5| 0.059| 0.13| ✓
SF-0603SP200R-2| 2.0| 0.033| 0.21| ✓
SF-0603SP300R-2| 3.0| 0.0159| 0.71| ✓
SF-0603SP400R-2| 4.0| 0.01| 0.96| ✓
SF-0603SP500R-2| 5.0| 0.00677| 2.05| ✓
SF-0603SP600R-2| 6.0| 0.0063| 3.47| ✓
SF-0603SP700R-2| 7.0| 0.0047| 5.04| ✓
SF-0603SP800R-2| 8.0| 0.0043| 6.5| ✓

AMBIENT TEMPERATURE AND TEMPERATURE DERATING

The current carrying capability of a fuse is determined by its performance during testing conducted at a specific ambient temperature of 25 °C. However, the operating life of a fuse is known to be significantly affected by changes in ambient temperature. As temperature increases, a fuse’s operating life is reduced, making the derating curve an essential consideration when selecting a fuse.
To compare the derating curves of five SinglFuse™ SMD Fuses, please refer to Figure 1.

Figure 1 – Temperature derating curves of SinglFuse™ SMD Fuses

MELTING INTEGRAL (I2 t) AND INRUSH CURRENT

Melting Integral (I2 t) and Inrush Current is influenced by various factors such as construction, material, pattern design and crosssectional area. Bourns SinglFuse™ SMD Fuses incorporate seven distinct technologies, each featuring a unique construction and corresponding I2 t value. As an illustration, SF- 0603SPA200R-2 exhibits a typical I2 t value of 0.21 (at 1 ms pre-arcing time) as specified in the datasheet.

Model| Rated Current (A)| Resistance (Ω) Typ. 1| Rated Voltage 1| Interrupting Rating| Typical I 2t (A2s)2| Agency Recognition
---|---|---|---|---|---|---
cUL: E198545
SF-0603SP100R-2| 1.0| 0.115| 63 VDC| 50 A @ 63 VDC| 0.059| ✓
SF-0603SP150R-2| 1.5| 0.059| 0.13| ✓
SF-0603SP200R-2| 2.0| 0.033| 0.21| ✓
SF-0603SP300R-2| 3.0| 0.0159| 0.71| ✓
SF-0603SP400R-2| 4.0| 0.01| 0.96| ✓
SF-0603SP500R-2| 5.0| 0.00677| 2.05| ✓
SF-0603SP600R-2| 6.0| 0.0063| 3.47| ✓
SF-0603SP700R-2| 7.0| 0.0047| 5.04| ✓
SF-0603SP800R-2| 8.0| 0.0043| 6.5| ✓

When an overcurrent event occurs, it generates thermal energy. If the duration of this event is brief, it can be likened to an inrush current, and the energy produced can be estimated by the area of the waveform displayed in Figure 2.

Figure 2 – Inrush waveforms and I2 t calculations

To prevent premature failure of a fuse element, it is important to consider the effect of inrush current even when it does not cause  melting of the fuse. In order to select a fuse with appropriate inrush withstand capability, it is necessary to calculate the circuit’s inrush energy and compare it with the melting time and I 2 t curve of the fuse.
The fuse’s melting I2 t value must be equal to or greater than the product of the inrush I2 t and a fuse derating factor (as shown in Figure 3) to ensure proper sizing and to avoid early failure.

Figure 3 – I2 t derating vs. inrush current withstanding number

FUSING CHARACTERISTICS AND TIME-CURRENT CURVE

The DC time-current characteristic of a fuse depicts the relationship between its pre-arcing time and the current flowing through it. This characteristic is instrumental in selecting a fuse with the desired fusing time, as fuses with the same current rating can have different time-current characteristics.

In the case of SF-0603SP200R-2, which falls under the category of 1 second to 120 seconds fusing characteristics, applying 4 A current would result in an average pre-arcing time of approximately 3.5 seconds.
Product Selection Guide Bourns® SinglFuse™ SMD Fuses FUSING CHARACTERISTICS AND TIME-CURRENT CURVE SF-0603SP-R S

Clearing Time Characteristics for Series

Average Pre-Arcing Time vs. Current Curves

PARAMETRIC SEARCH TOOL

The Parametric Search tool available online simplifies the selection process.
To access more details about these products, please refer to the Bourns® SinglFuse™ SMD Fuse Technical Library

PRACTICAL EXAMPLE:

When the inrush is present, follow Step A to B to C When the inrush is negligible or absent, follow Step A to C

Instruction

www.bourns.com

References

• P65Warnings.ca.gov

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